FARM NOTES

Putaruru Press, Volume IV, Issue 125, 25 March 1926, Page 6

FARM NOTES

GONTAGiOUS MAMMITIS.

IN DAIRY COWS. Some Valuable Observations. {By C. S. M. Hopkirk, B.V.Sc. (Melb.), Officer in Charge, Veterinary Laboratory, Wallaceville, in the Journal of Agriculture). The present time ■ appears to be opportune for offering a few observations on the disease contagious mammitis, a subject which is attracting attention throughout the dairying districts of New Zealand, having been brought to the fore by the various cures and prophylactics on the market, more especially by the use of vaccines. These observations are based on the examination of thousands of samples from New Zealand cows, on cultural work in the laboratory, and on watching the course of the disease in experimental animals—giving confidence to express an opinion on many points met with. CAUSE. It may be remarked in the first place that the name “contagious mammitis ” is really a misnomer, as it will not be contested by any veterinary practitioner that all forms are contagious given certain conditions. Mammitis may be caused by several species of organisms, either singly or together, those which have been definitely found in New Zealand being streptococci, a staphylococcus, and two forms of rod-shaped bacteria. We may ignore the rod-shaped group, and consider the remaining two. Staphylococci are frequently found in the undrawn milk of cows, lying harmlessly in the large milk-sinuses. Staphylococci and the bacillus of abortion, according to one outhority, are found more often than are streptococci or chain forms, but this has not been our experience in New Zealand. When inflammation of the quarter has actually developed it is not very frequently the staphylococcus which is found to be present. Occasionally the writer has come across this organism in pure culture, more particularly with goats. Whenever alone causative, it is found in large numbers in the samples submitted, and is obtained in pure culture from the sample taken in aseptic manner. The streptococcus, on the other hand, is far and away the most frequent type to be met with here.

Now, several different varieties of streptococci may be, found in mammitis, and the streptococcic form is that which we are used to hearing- called “ contagious mammitis.” It is known that even the streptococcus of sour milk may set up mammitis, and it appears certain from experimental work that there is a particular streptococcus from the droppings of cows which frequently causes a less virulent form of the disease. The most typical variety, however, is that known as Streptococcus mastitidis, which has definite reactions in culture media. The virulence of the organism found in any one outbreak of the disease is a factor when it comes to controlling that outbreak, but the biggest factor is that of injury to the udder. Injury may be brought about in many and various ways, among which may be enumerated chills, calving, horning, kicks, falls, possibly septic metritis, cow-pox, rough handling of ucfder, irregular milking, heavy production, and overstocking with milk before calving, but, above all, to machine milking. Certainly contagious mammitis was known before machine milking, but not to the extraordinary extent that it is known to-day through injurious and careless use of the machines. A machine correctly handled is not a source of danger, but undue increase of vacuum, failure to understand the individual peculiarities of all cows in the herd, and also the difficulty with many farmers to keep their machines scrupulously clean, tend by, continuous irritation and by combining the two necessary factors in this dease—dirt containing the streptococcus and local injury—to be the source of apparently violent outbreaks of contagious mammitis. To recapitulate, we have three factors—the streptococcus which is apparently unibiquitous in cowsheds, the virulence of that organism ip a given outbreak, and, thirdly, of most importance, injury to the delicate tissues of the quarter. COURSE OF THE DISEASE. The majority of cases of contagious mammitis commence as noticeable acute inflammatory reactions in one or more quarters of the udder. In this quarter one usually gets a sudden change in the milk owing to the large number of invading wandering cells from the blood-stream, and owing to an inflow of lymph which will alter the reaction of the milk. In the worst cases inflammation stops the milk-secretion to a large extent, and in place of milk one gets yellow fibrinous clots and an amber-coloured

fluid. In milder cases a deposit of cells is found at the bottom of the sample to be examined, the secretion having- retained its milky colour to some extent but appearing thin and watery. There is, however, another form which occurs commonly and which is annoying when curative measures are adopted; it is also annoying to the examiner of the sample in that, unless a thorough history of the cow is supplied, he is not absolutely sure of his diagnosis without ample experience; moreover, it is dangerous in that the condition is often not recognised by the milker. By this is meant the common chill whicth persists as a more or less subacute form of the disease for some considerable time. This type does not flare up into an acute attack when first attacking' the quarter, and is, the writer believes, a combination of slight injury to the quarter and slight virulence of the organism. Of recent years this type been common. But let a quarter such as this be left without milking—as during the drying-off period—then the disease may often flare up and assume every indication of a really acute form. Streptococcic mammitis runs one of several courses. In one the number of cells quickly subsides, and the milk reassumes a normal state to the naked eye. This may be due to the individual resistance of the cow or to the fact that a less virulent species of the streptococcus has gained entrance to the quarter. In afiother form of outbreak the quarters quickly become dry, the fat-cells are ruined, and the quarter becomes hard and fibrous, never again becoming quite normal, although at next lactation there may be some return to milk. A third type results in a fibrous lump forming at the base of the teat-sinus—the popular “ pea in the teat.” Yet another case will continue to give a secretion rich in inflammatory cells, and obviously affected with the disease, for months or even throughout the animal’s lactation period. All these cases harbour the streptococcMs. Where a staphylococcus is found in pure culture or in a rich combination with the streptococcus in an acute case there is often abscess-formation and sloughing of the quarter. When an attack has been running its course for .some time one finds that the infection becomes mixed—that is, streptococci are joined by staphylococci, which may help to prolong the condition.

A large number of cases of contagious mammitis appear themselves to subside, with or without treatment, into what may be called a chronic state, in which one gets a few inflammatory cells always present in the cream on standing, and in which cells one may often see microscopically an engulfed streptococcus. These cases— and the writer believes them to be the majority of cases of contagious mammitis last usually throughout that paricular lactation period. Once, however, the cow has dried off successfully, without a recurrence of the acute form, streptococcus, which has been lying almost latent, dies out, and the cow usually comes in with a sound quarter. She may not, of course, give the old quantity of milk, but what she gives is wholesome. As it requires the microscope to demonstrate the case of these cows, and as they are perfectly normal to all outward appearance, the farmer may well understand how dangerous they are in his herd. It is such cows which keep up the incidence of mammitis in the herd.

To show that this view of chronic •mammitis is correct an actual instance may be given. Ten cows were known to have had contagious mammitis in definite quarters in the past two to six months, and then, giving only an odd inflammatory cell in the milk, were left over two milkings, except where easement was given to one or two animals which were becoming overstocked. The collection of milk at bodytemperature gave the organisms lying latent an opportunity to propagate under ideal conditions. In whichever quarters these cows had had mammitis it was observed that they had a recurrence in the form of a very acute attack, and. what was more significant, only in those same quarters. The previously normal quarters remained normal. The obvious conclusion is that the affected quarters should either have a treatment given which might kill the streptococcus, or else that such quarters should be dried off. TREATMENT. The matter of treatment may be dealt with under two heads—namely, curative methods and prevention. Curative methods so far have not been as successful as might be expected, and many drugs have been tried. The ideal is a drug which could be easily administered and which would be exerted by the udder without harm in the cow. but would h#?™ p harmful action on bacterial life only. No drug of this nature has yet been discovered. Failing such a drug, one can try the next best me-

thod, and that the writer believes to be I pumping in or otherwise introducing* a f disinfectant in gaseous form. Provid- j ed the disease is taken in time, and , the quarter thoroughly stripped by massage to remove clots, some good . results have been obtained in many ' cases by such methods, but even then at least two treatments are found to be more satisfactory, with an interval of about three days between them. There are cures on the market embodying this principle, but even the best of these cannot be held as “ curealls.” Prevention is truly better than cure. The farmer to a large extent has this in his own hands, and the methods are cleanliness of the shed and utensils, | care in handling the cows and milking ' machines, and care in buying in cows for the herd. There are many herds throughout the country which never or rarely contract mammitis. Handmilked herds— including many pedigree herds which do not risk machines or, if they use them, do so with scrupulous care—often enjoy a welcome freedom from the disease. This is largely due to milking each cow as she requires to be milked, and not treating every one as a machine built on the same pattern. I VACCINES. The preventive method now before dairy farmers in the form of vaccine is still in the experimental stage. If inoculation is a means of protecting the majority of cows from mammitis, 1 then one would expect that cows which are actually or chronically affected, and which therefore harbour many millions of organisms, should produce in themselves sufficient immunity to protect themselves from the ravages of the organism in a second quarter. One knows, however, that it is just as easy for a cow already affected in , one quarter to be later affected in a . second as it is for the primary infection to become established, and that although protective antibodies are produced they are not sufficient to keep the cow from becoming infected. This fact is a definite contradiction to the use of vaccine in connection with streptococcic mammitis. 'Experimental work at this Laboratory has given us no feeling of security with the vaccines now in local use. It is said by the advocates of vaccine that the artificial inoculation of the j disease into the udder for the purpose of testing is too severe to show pro- j tection or otherwise of a vaccine. Suppose, for argument’s sake, that this is granted, yet the experiments i are particularly valuable in that they | show that the length of time for which animals remain affected is not greater in non-vaccinated control animals than in vaccinated, and surely the vaccinated should clean up very much quicker. This is also, to the writer’s mind, another point which cannot be overlooked by advocates of the vaccine method of prevention. Much capital has been made of this Department’s method of experimentation, but even though the primary dosage directly placed in the udder was higher than would be the case with natural infection, yet if the control cows can throw off infection as quickly and as effectively as vaccinated cows it is obvious that the vaccinated cows are not benefited to any noticeable extent by the vaccine.

It is not only in the experimental work at Wallaceville and at Ruakura but in the field that we find the vaccine has not been effective in producing the necessary 'immunity to protect herds. A mass of information has been obtained by officers of the Department, and they find that in a great many the cows vaccinated have not received sufficient immunity to prevent infection. This is particularly noticeable in the Wairarapa, and this district, owing* to shortage of rain, has not had the flush of milk in the current season which some other districts have had, and without this flush of milk we could not expect the same prevalence of mammitis. There is a blood test (the agglutination test) which can be applied to a cow’s blood to show what amount of a certain antibody is set up by the presence of the streptococci in the system of a cow. The amount set up in experimental vaccinated cows was found to be very much less than where the cows were affected with the chronic form of the disease, these latter cows not having been vaccinated. This would tend to show that a cow chronically affected, has a better opportunity of withstanding further invasion by the disease, but, as was stated before, such cows often do become infected in a further quarter. How much easier, then, would it be for the vaccinated cow, with less immunity, to take the disease. CONCLUSION. There is one great danger which the. farmer should be warned against, and that is the laxity which may follow his belief in a preventive agent against contagious mammitis. Sooner or later he may receive a severe lesson. Should he, on the other hand, knowing the wide-spread nature of the

organism of the disease, keep up strenuous endeavours by cleanliness and watchfulness to avoid his cows becoming- infected, then he will correspondingly benefit. The farmer who will have least trouble is he who milks carefully to avoid injury, builds up the system of his cows by good feeding and suitable top-dressing of his land to withstand -disease, keeps his utensils clean, avoids risks of infection by strict antiseptic precautions, and buys in only cows free from diseases of the udder.